More particularly, in this connection, a centrifugal rotor is concerned which is included in a centrifugal separator comprising also an inlet device, which has an inlet channel and is arranged during normal operation of the centrifugal separator to supply into the inlet chamber through the inlet channel a predetermined flow of said liquid to be treated in the centrifugal rotor, and an outlet device which has at least one outlet channel and is arranged during normal operation of the centrifugal separator to discharge through the outlet channel a separated liquid from a first radial level in the outlet chamber out of the centrifugal rotor. Furthermore, the centrifugal separator comprises for internal cleaning of the centrifugal rotor a cleaning device including means for supply of a cleaning liquid to the interior of the centrifugal rotor, means for enabling movement of a liquid surface, formed within the outlet chamber at said first radial level during rotation of the centrifugal rotor, in a direction towards the center axis of the centrifugal rotor and at least one reconducting member, which delimits at least one reconducting channel having two ends and which is formed to be placed such that the reconducting channel opens with its one end in the outlet chamber at a second radial level, that is situated between the center axis of the centrifugal rotor and said first radial level, and opens with its other end in the inlet chamber.
A centrifugal separator of this kind is described in DE-30 41 210-C2. In this known centrifugal separator the reconducting member is intended and formed particularly for enabling cleaning of certain central parts of the centrifugal rotor, which are situated in the area of the inlet device extending into the inlet chamber. The reconducting member, is not, however, intended or formed for enabling cleaning of other parts of the centrifugal rotor, e.g. parts delimiting the main part of the inlet chamber, the separation chamber and the outlet chamber. For cleaning of these other parts of the centrifugal rotor use is instead made of the ordinary outlet device for liquid having been separated in the centrifugal rotor. Thus, a cleaning liquid is conducted during the cleaning operation out of the outlet chamber through the outlet channel and then again into the centrifugal rotor through said inlet channel. The recirculation flow of cleaning liquid through the outlet and inlet channels is then substantially larger than the flow of cleaning liquid passing through the reconducting channel.
For accomplishing an effective cleaning of the inlet, separation and outlet chambers of the rotor it is important that the flow of cleaning liquid through the centrifugal rotor is large. Thus, sometimes such a flow of cleaning liquid has to be several times larger than the flow of liquid flowing through the centrifugal rotor during the normal-use thereof. By means of an arrangement of the kind described in DE-30 41 210-C2 it is certainly possible to accomplish a relatively large circulation flow of cleaning liquid through the centrifugal rotor. A precondition for this is only that the outlet and inlet devices used for the recirculation are dimensioned for such a large circulation flow. However, this is not normally the case in practice, and the background thereof is the following.
It is important that an outlet device of the kind here in question is dimensioned with regard to the size of the flow for which it is intended. The outlet device, which is partly constituted by a stationary member freely suspended within the rotating centrifugal rotor and which together with the centrifugal rotor forms a pump, thus should not be over-dimensioned, i.e. be given a too large flow capacity. If, namely, at normal rotational speed of the centrifugal rotor, the outlet device is used for a flow that is much smaller than the flow for its maximum capacity, there will come up undesired flow phenomena within and around the outlet device in the centrifugal rotor. These can lead to vibrations of the outlet device and, in the worst case, also influence the centrifugal rotor to perform swinging motions.
This means that circulation flow cleaning of a centrifugal rotor, as such cleaning has been described in DE-30 41 210-C2, can normally be formed in practice only by means of a circulation flow having the same magnitude as, or being insignificantly larger than, the flow through the centrifugal rotor at its normal use, since the outlet device is not normally dimensioned for a flow substantially larger than that.
Furthermore, if in an arrangement according to DE-30 41 210-C2 a circulation flow several times larger than the normal flow through the outlet device should be possible, also those parts of the outlet device situated outside the centrifugal rotor would have to be dimensioned for a substantially larger flow than they normally are.
For avoiding the disadvantages connected with conventional circulation flow cleaning in accordance with DE-30 41 210-C2, an arrangement in accordance with DE-38 02 306 could be used instead. An arrangement of this kind requires, however, that the centrifugal rotor is stopped after the finished separating operation and that, among other things, parts of the centrifugal rotor are exchanged, after which circulation flow cleaning of the centrifugal rotor can be beformed by means of a special recirculation member dimensioned with regard to a desired circulation flow of cleaning liquid. An arrangement of this kind has obvious disadvantages and is not suitable in a process industry having requirements on automatically beformable cleaning operations without need of manual handling of the centrifugal rotor.